1. Field of the Invention
This invention relates generally to the field of apparatus for use in the installation of an elongated post in the ground to stabilize the post in an upright position, and more particularly to a ground stabilization apparatus that outwardly distributes forces applied by the post into the substrate in which it is embedded.
2. Background Art
It has long been recognized that an elongated fence post that is simply buried in dirt hole will begin to lean over time. Eventually, the lean becomes extreme enough that the fence has to be replaced because of aesthetic or structural considerations. The solution in the background art has been to hinder the movement of the post by attaching an apparatus to its base end before that end is buried in the dirt. The added surface area of these apparatus provides extra resistance against the dirt surrounding it.
An example of this type of device is found in a 1903 patent granted to Harbold. In this patent, U.S. Pat. No. 720,025 taught attaching two sets of cross members to two sides of the bottom of the fence post before burying it. The post is further braced by a cable that loops around the top of the post and descends outwardly toward the ground where it is held by anchor bars that are also designed to resist pulling from the ground by having a relatively large surface area held by the force of the dirt in which it is buried.
This concept of increasing the surface area of the base of the post in an effort to increase resistance is also found in U.S. Pat. No. 1,025,823 (Morrow). In Morrow, the post is designed to support horizontally mounted plates at a variety of depths along the buried portion of the post. U.S. Pat. No. 897,417 granted to Self adds surface area at variety of depths along the buried portion of telephone poles. This surface area adding apparatus is comprised of an upper cylindrical collar with a flanged base that is attached to the bottom end of a telephone pole. The flange portion of the base is covered with dirt, partially filling the hole, where a second surface area increasing member is attached to the upper collar portion of the base. The end of the telephone pole is secured within the collar flange and the device is then fully buried.
Two other devices to increase the surface area of the base of a rod or post are found in U.S. Pat. No. 1,433,621 (Hutton) and U.S. Pat. No. 4,269,010 (Glass). The device taught in Hutton is comprised of a base plate with four upwardly extending concrete reinforcing fins that converge to a vertical central collar. This central collar holds the base of the rod. This entire anchor assembly is then buried in a hole dug large enough to accommodate the entire apparatus. Another finned device is taught in U.S. Pat. No. 4,269,010 (Glass). This device has a central plate with an opening through which the base of the post is firmly gripped by a plurality of radially spaced, elongated vertical splines. Several of these devices are buried at different depths along the base portion of the post.
While the patents above all take advantage of their extra surface area to act as a resistance against the soil in which they are buried, the problem is that the ability of the soil to counter the resistive force of these devices is severely compromised by the very fact that a great deal of the naturally compacted dirt has to be removed in order to place these devices into the hole. The dirt is then replaced over the resistance members and tamped down. It is probable that it will take months, if not years, for the soil to regain the compaction that it possessed before it was disturbed in order to bury these devices.
One patent that recognized the problem of losing the natural compaction of the dirt when a hole is dug for the post is U.S. Pat. No. 3,115,226 (Thomson). In this patent, Thomson teaches a device that does not require a large hole to be dug. Instead, a collar is driven into the ground where an explosive charge is detonated in its end to form an underground cavern. The post assembly is placed into the collar where a set of spring loaded fins extend once they reach the open cavern. It is even suggested in the Thomson patent, just discussed, to fill the underground cavern with concrete by pouring it through the collar.
Despite the teaching of these patents, the preferred method of fence post installation is the pouring of concrete either around the base of the post, or filling the entire hole, commonly two to three feet deep with a diameter approximately twice that of the post, with cement. Once the post is lowered into the hole, it is temporarily braced in an upright and plumb position using boards nailed to the post on one end and to stakes on the opposite end. Typically, between one and three sixty-pound bags of concrete are mixed and poured into each hole. The concrete is then allowed to dry for two days or more. Once the concrete is set, the temporary bracing is removed and the partitions of the fence are constructed between the posts. A typical one-quarter acre lot requires approximately four hundred and twenty feet of fencing to surround it. This means that about fifty-five posts have to be installed with each requiring between one and three sixty-pound bags of concrete. With between a ton and a half and almost five tons of concrete required to install this relatively short fence, it is not hard to imagine the considerable amount of cost and effort that goes into the digging, concrete mixing, alignment and temporary bracing of the fence posts. And this method is the current state of the art in post installation.
Installation of fence posts in concrete is by its very nature a permanent installation-- permanent being until the fence needs to be replaced. To replace the post, one must typically dig out a two to three foot by eight inch concrete plug weighing at least sixty pounds, lift the old post and concrete plug from the hole, and then figuring out how to dispose of it. A new post is then set in the hole, which is now larger than the original installation, which means that an even greater quantity of cement is required to fill it. In some applications, a large quality of concrete is acceptable. For instance, U.S. Pat. No. 2,036,047 (Hill) teaches a design for a footing of a transmission tower that is meant to provide adequate surface area to create a firm anchorage when the backfill material, presumably concrete, is placed over the footing and tamped in place. For most installations, however, concrete is a little too permanent.
In some applications, concrete is not desirable because the installation of the post is only meant to be temporary. A primary example of this is a real estate sign. U.S. Pat. No. 5,082,231 (Knowles) attempts to meet this need where a device for the temporary placement of posts is described. This device includes a ground engaging portion that is comprised of three radially extending fins that taper to an axially aligned center point, much like an arrowhead used for hunting. At the upper junction of the three fins, similar to the where the shaft of an arrow would be placed, is a collar that receives the base of the fence post. The device is installed in the ground by placing a temporary driver cap into the collar and driving the point of the ground-engaging member into the ground using a mallet, probably better described as a sledge hammer. The cap is then removed and the lower portion of the post is secured into the collar.
A very similar concept was described in U.S. Pat. No. 4,271,646 and U.S. Pat. No. 4,588,157, both granted to Mills prior to the Knowles patent. The device described in these earlier patents seems to be an elongated version of the Knowles device. The ground engaging member of this device has a plurality of fins in a cruciform cross-section that taper to a point and an open box section mounted on the upward portion of the ground engaging member for reception of the bottom end of the post. The primary difference between the Mills and Knowles designs seems to be that Mills uses a piece of scrap lumber as an impact plug for driving the ground engaging member into the ground, while the Knowles design using a specially designed plug that can also be used to start a reception hole in the ground and can later be used as a cap when the post is not inserted into the upper collar portion. In both of these devices, the base of the post is secured inside the collar portion of the device. Mills bends tabs into the post, or in the production version currently on the market, uses a clamp at one corner of the collar to tighten the collar around the post.
U.S. Pat. No. 3,342,444 (Nelson) is another variation on the concept of driving a finned ground engaging member into the ground and then inserting the base of the post into an extended collar with three radially extending fins welded at equal distances around its circumference. Each of these three fins has a second fin mounted perpendicularly to the first at its upper end. This forms a space between the first and second fins that is roughly triangularly shaped and that is intended to act as a pincer that will grab roots and the like as it is driven into the ground.